Advertisements
Advertisements
Question
It is now believed that protons and neutrons (which constitute nuclei of ordinary matter) are themselves built out of more elementary units called quarks. A proton and a neutron consist of three quarks each. Two types of quarks, the so called ‘up’ quark (denoted by u) of charge (+2/3) e, and the ‘down’ quark (denoted by d) of charge (−1/3) e, together with electrons build up ordinary matter. (Quarks of other types have also been found which give rise to different unusual varieties of matter.) Suggest a possible quark composition of a proton and neutron.
Solution
A proton has three quarks. Let there be n up quarks in a proton, each having a charge of `+2/3"e"`.
Charge due to n up quarks = `(2/3"e")` n
Number of down quarks in a proton = 3 − n
Each down quark has a charge of `-1/3"e"`.
Charge due to (3 − n) down quarks = `(-1/3"e")(3 - "n")`
Total charge on a proton = + e
∴ `"e" = (2/3"e")"n" + (-1/3"e")(3 - "n")`
`"e" = ((2"ne")/3)-"e" + ("ne")/3`
2e = ne
n = 2
Number of up quarks in a proton, n = 2
Number of down quarks in a proton = 3 − n = 3 − 2 = 1
Therefore, a proton can be represented as ‘uud’.
A neutron also has three quarks. Let there be n up quarks in a neutron, each having a charge of `+3/2"e"`.
Charge on a neutron due to n up quarks = `(+3/2"e")"n"`
The number of down quarks is 3 − n, each having a charge of `(-1/3)"e"`.
Charge on a neutron due to `(3 - "n")`down quarks = `(-1/3"e")(3 - "n")`
Total charge on a neutron = 0
`0 = (2/3"e")"n" + (-1/3"e")(3 - "n")`
`0 = 2/3 "en" -"e" + ("ne")/3`
e = ne
n = 1
Number of up quarks in a neutron, n = 1
Number of down quarks in a neutron = 3 − n = 2
Therefore, a neutron can be represented as ‘udd’.
APPEARS IN
RELATED QUESTIONS
Explain the meaning of the statement ‘electric charge of a body is quantised’.
Does the charge given to a metallic sphere depend on whether it is hollow or solid? Give reason for your answer.
Consider the situation shown in the figure. What are the signs of q1 and q2? If the lines are drawn in proportion to the charges, what is the ratio q1/q2?
When a charged comb is brought near a small piece of paper, it attracts the piece. Does the paper become charged when the comb is brought near it?
Choose the correct option.
Two charges of 1.0 C each are placed one meter apart in free space. The force between them will be
A metallic sphere A isolated from ground is charged to +50 μC. This sphere is brought in contact with other isolated metallics sphere B of half the radius of sphere A. The charge on the two-sphere will be now in the ratio
Choose the correct option.
Two-point charges of A = +5.0 μC and B = -5.0 μC are separated by 5.0 cm. A point charge C = 1.0 μC is placed at 3.0 cm away from the centre on the perpendicular bisector of the line joining the two point charges. The charge at C will experience a force directed towards
Answer the following question.
State the law of conservation of charge.
+2 C and +6 C two charges are repelling each other with a force of 12 N. If each charge is given -2 C of charge, then the value of the force will be ______
Conservation of charges in tribo electric charging _________.
Charge is quantized means ______.
Eight dipoles of charge of magnitude ± e are placed inside a cube. The total electric flux coming out of the cube will be:-
A glass rod rubbed with silk is used to charge a gold-leaf electroscope and the leaves are observed to diverge. The electroscope thus charged is exposed to X-rays for a short period. Then ______
A paisa coin is made up of Al-Mg alloy and weighs 0.75g. It has a square shape and its diagonal measures 17 mm. It is electrically neutral and contains equal amounts of positive and negative charges.
Treating the paisa coins made up of only Al, find the magnitude of equal number of positive and negative charges. What conclusion do you draw from this magnitude?
Consider a coin of Example 1.20. It is electrically neutral and contains equal amounts of positive and negative charge of magnitude 34.8 kC. Suppose that these equal charges were concentrated in two point charges seperated by (i) 1 cm `(∼ 1/2 xx "diagonal of the one paisa coin")`, (ii) 100 m (~ length of a long 6 building) and (iii) 106 m (radius of the earth). Find the force on each such point charge in each of the three cases. What do you conclude from these results?
Figure represents a crystal unit of cesium chloride, CsCl. The cesium atoms, represented by open circles are situated at the corners of a cube of side 0.40 nm, whereas a Cl atom is situated at the centre of the cube.
The Cs atoms are deficient in one electron while the Cl atom carries an excess electron.
- What is the net electric field on the Cl atom due to eight Cs atoms?
- Suppose that the Cs atom at the corner A is missing. What is the net force now on the Cl atom due to seven remaining Cs atoms?
Two fixed, identical conducting plates (α and β), each of surface area S are charged to –Q and q, respectively, where Q > q > 0. A third identical plate (γ), free to move is located on the other side of the plate with charge q at a distance d (Figure). The third plate is released and collides with the plate β. Assume the collision is elastic and the time of collision is sufficient to redistribute charge amongst β and γ.
- Find the electric field acting on the plate γ before collision.
- Find the charges on β and γ after the collision.
- Find the velocity of the plate γ after the collision and at a distance d from the plate β.
